EarthRef.org Reference Database (ERR) -- Bian et al. 2001

Bian, L., Hinrichs, K., Xie, T., Brassell, S.C., Iversen, N., Fossing, H., J\orgensen, B.B. and Hayes, J.M. (2001). Algal and archaeal polyisoprenoids in a recent marine sediment: Molecular isotopic evidence for anaerobic oxidation of methane. Geochemistry Geophysics Geosystems 2. doi: 10.1029/2000GC000112. issn: 1525-2027.

Analyses of 13C contents of individual organic molecules in a marine sediment show that crocetane, 2,6,11,15-tetramethylhexadecane, an isomer of phytane, is produced by microorganisms that use methane as their main source of carbon. The sediments lie at a water depth of 68 m in the Kattegat, the strait between Denmark and Sweden. Crocetane appears first 185 cm below the sediment-water interface, in the zone marking the transition from sulfate reduction to methanogenesis. Its 13C value is -90 ? 10 ? versus Vienna Pee Dee Belemnite (VPDB). Its structure, which includes four isoprene units arranged symmetrically around a tail-to-tail linkage, suggests that it is produced by a member of the archaea. Growing at the intersection of the diffusion gradients for sulfate and methane in sedimentary pore waters, the source organism apparently functions as a methane-consuming member of the microbial consortium responsible for the anaerobic oxidation of methane , in which, as first demonstrated quantitatively in these sediments , electrons are transferred from methane to sulfate. The presence of archaeal biomass throughout the sediment section is indicated by significant concentrations of 2,6,10,15,19-pentamethylicosane (PMI) and of ether-bound phytane and biphytane. The PMI reaches a minimum value of -47 ? well below the transition zone. Its isotopic depletion could reflect either methanogenic or methanotrophic sources. The ether-bound lipids are isotopically uniform throughout the section and are presumed to derive from archaea that utilize a carbon source unaffected by the oxidation of methane.